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47 lines
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Markdown
Executable File
47 lines
1.2 KiB
Markdown
Executable File
# [98. Validate Binary Search Tree](https://leetcode.com/problems/validate-binary-search-tree/)
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## 题目
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Given a binary tree, determine if it is a valid binary search tree (BST).
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Assume a BST is defined as follows:
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- The left subtree of a node contains only nodes with keys **less than** the node's key.
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- The right subtree of a node contains only nodes with keys **greater than** the node's key.
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- Both the left and right subtrees must also be binary search trees.
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**xample 1:**
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2
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/ \
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1 3
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Input: [2,1,3]
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Output: true
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**Example 2:**
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5
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1 4
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/ \
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3 6
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Input: [5,1,4,null,null,3,6]
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Output: false
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Explanation: The root node's value is 5 but its right child's value is 4.
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## 题目大意
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给定一个二叉树，判断其是否是一个有效的二叉搜索树。假设一个二叉搜索树具有如下特征：
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- 节点的左子树只包含小于当前节点的数。
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- 节点的右子树只包含大于当前节点的数。
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- 所有左子树和右子树自身必须也是二叉搜索树。
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## 解题思路
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- 判断一个树是否是 BST，按照定义递归判断即可
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